Flexible molded polyurethane foam requires mechanical crushing to open foam cells and prevent shrinkage and to improve dimensional stability of the foam pad. Current mechanical methods for cell opening consist mainly of crushing, vacuum rupture or time pressure release.
Upon demold, mechanically crushing and breaking the polyurethane foam cells enables the polyurethane foam to be more dimensionally stable. Another method of breaking the cells is vacuum crushing which involves drawing a vacuum on the finished polyurethane foam causing cell rupture. The overall effect of these methods is reduced foam shrinkage.
Other mechanical attempts have been made to achieve dimensionally stable foam, such as decreasing cycle production times. For example, demolding the polyurethane foam in three minutes as compared to four minutes will dramatically improve the dimensional stability. Another method for producing dimensionally stable foam is time pressure release (TPR). TPR comprises opening the mold during the curing process to release the internal pressure and then reclosing for the duration of the cure time. The sudden release of the internally generated pressure bursts the cell windows, thereby obtaining an open cell foam.
Mechanical methods usually result in incomplete or inconsistent cell opening and require a flexible molded foam producer to invest in additional machinery. A chemical method for cell opening would be preferred.
The current chemical methods all have drawbacks such as requiring high levels (often as high as 1-5 pphpp) or adversely affecting the foam physical properties.
U.S. Pat. No. 3,314,834 discloses that diketo compounds form effective potlife extension agents in polyurethane propellants.
U.S. Pat. No. 3,635,906 discloses certain chelate-forming compounds have the effect of delaying initiation of reaction between an organic polyisocyanate and an organic polyhydroxy compound in the presence of an amine-free organotin cure rate catalyst, thereby extending the pot life of the reaction medium without retarding the rate of cure.
U.S. Pat. No. 4,426,510 discloses coating or adhesive compositions having extended potlife and short cure time comprising an organic polyol, an organic polyisocyanate, an organozinc cure rate catalyst, and a compound selected from (a) beta-dicarbonyl compounds, (b) alpha-hydroxy ketones, (c) fused aromatic beta-hydroxy ketones, and (d) beta-hydroxy nitrogen-heterocyclic fused aromatics.
GB 2,303,372 discloses making polyurethane foams using the mechanical frothing technique and a catalyst system comprising a metal acetyl acetonate and acetyl acetone. It is suggested that the invention can benefit chemically frothed urethane foams and non-foamed polyurethane.
U.S. Pat. No. 4,721,642 discloses a blocked polyisocyanate prepolymer formed by blocking the terminal --NCO group of the polyisocyanate with a blocking agent such as, alcohol, phenols, ethyl acetoacetate, .epsilon.-caprolactam, MEK oxime, diethyl malonate, acetoacetone, cyanic acid, and sodium bisulfite. A polyurethane resin foamable paint comprises an aqueous dispersion composed of blocked polyisocyanate prepolymer, additives, chain extender, foaming agent and emulsifier.
CA 2,141,890 discloses the production of rigid polyurethane, polyisocyanurate and polyurethane urea foams with HCFC blowing agents and optionally a flame retardant and/or chelating agent which is acidic, i.e., having a pKa value from 0 to 10.
U.S. Pat. No. 3,972,846 discloses a curable polyurethane composition comprising a keto compound and a liquid mixture of an organic aliphatic polyfunctional polyisocyanate and a compound having active hydrogen. The curable polyurethane composition is characterized by exhibiting a long pot life due to the presence of the keto compound.
U.S. Pat. No. 4,251,635 discloses flexible polyurethane foam having reduced tendency to form burning embers when it is ignited and burned by incorporating a ketone or benzaldehyde into the reaction mixture before foaming.
DE 1 005 722 discloses reactions of polyols with polyisocyanates can be retarded by adding an imine (the condensation product of a primary amine and an aldehyde, ketone or diketone).
DE 2 451 726 discloses a process for slowing down the reaction of isocyanate compounds with polyester polyols in which the polyols contain at least one aldehyde and/or ketone and a mono-amine in the molar ratio of aldehyde or ketone group: amino group from 1:0.1 to 1.